The subjective components of the Disease Activity Score 28-joints (DAS28) in rheumatoid arthritis patients and coexisting fibromyalgia

To determine the contribution of fibromyalgia (FM) to the subjective components of the Disease Activity Score 28-joints (DAS28) in patients with rheumatoid arthritis (RA), and to analyse the discriminatory performance of the derived DAS28 patient-reported components (DAS28-P) to identify patients with fibromyalgic RA. Consecutive RA patients underwent clinical and clinimetric assessment. The DAS28-P index was derived from the components of the DAS28 scores by rearranging the DAS28-ESR formula. Patients were distinguished by the presence of FM. Student parametric t tests or Mann-Whitney non-parametric U tests were used to determine any between-group differences. Receiver operating characteristic (ROC) curve analysis was used to test the ability of the DAS28-P index to distinguish patients with RA and those with fibromyalgic RA. The study involved 292 RA patients (80.5% females, mean age 63 years) with a mean disease duration of 11.6 ± 8.5 years. Forty-three patients (14.7%) had concomitant FM, and significantly higher tender joint count (p < 0.001), pain numerical rating scale, global health status (p = 0.007), and DAS28 scores (p = 0.006) than those without FM. The DAS28-P values were also significantly higher in the patients with FM (0.68 ± 0.09 vs 0.58 ± 0.06; p < 0.001). The discriminatory power of the DAS28-P was very good (area under the ROC of 0.858, optimal cut-off value of 0.631). The presence of FM strongly influences the DAS28 results. The assessment of patient-reported components to the DAS28 through the DAS28-P can be a useful way to identify patients with fibromyalgic RA.